Did a little experimenting. It seems like using the ethernet adapter does help to reduce input lag a little, but it's not enough for me to be sure that it wasn't just a placebo effect. However, I still had several moments where the game stuttered or froze for a few seconds. I think that no matter how stable your connection is, your experience will still depend on the other player(s).

Normally Smultimate doesn't let you taunt in online quickplay (which is DUMB), but I found out that the patch released today lets Kirby taunt when he has a copied ability, because otherwise he had no way to get rid of it.
Now the Kirby mains alone shall style all over their opponents!

Also if you think the game a port I suggest you read up on the many mechanic, gameplay, and character balance changes. This is no longer E3 2018 and it's become very clear that there is much to separate this game from Smash 4. It plays very differently.